1. Field of Art
The present invention relates to depositing one or more layers of barrier materials on a substrate using atomic layer deposition (ALD).
2. Description of the Related Art
Some devices (e.g., integrated circuits) are sensitive to elements such as moisture and oxygen present in atmosphere. In order to protect such devices, the devices are often encapsulated in layers of barrier materials during the fabrication process. The layers are generally formed over the devices and extend over the edges of the devices to prevent such elements from coming into contact with the devices. The films are often formed using methods such as sputtering or chemical vapor deposition (CVD). One example of such barrier layer is aluminum oxide (Al2O3).
Figure (FIG. 1 is a cross sectional diagram illustrating a device 136 encapsulated in two barrier layers 124, 132, and an intermediate layer 128 between the two barrier layers. The intermediate layer 128 may, for example, serve to flatten the vertical profile of the device 136 and barrier layers 124, 132 deposited thereon. During the deposition of the barrier layers 124, 132 and the intermediate layer 128, a shadow mask 110 is placed on a substrate 120. The shadow mask 110 has openings so that the areas to be deposited with barrier layers 124, 132 and the intermediate layer 238 are exposed. Since materials for deposition are injected vertically into the opening of the shadow mask 110, the barrier layers 124, 132 and the intermediate layer 128 extend generally to the same horizontal edges 130.
As illustrated, the intermediate layer 128 and the barrier layer 124 do not extend beyond the barrier layer 132. The moisture or oxygen can penetrate the layers 124, 132 at the edges 130 since the coverage of the layers 124, 132 is incomplete at the edges 130. Hence, the barrier layers 124, 132 formed on the device 136 may provide inadequate shielding against atmospheric elements. Moreover, if the barrier layers extend over to the shadow mask 110, the barrier layers 124, 132 may come in contact with the shadow mask 110 and can be ruptured or torn apart when the shadow mask 110 is removed from the substrate 120.
Barrier layers formed by conventional deposition methods are also vulnerable to other defects. FIG. 2 is an example of a device 234 with a transparent electrode 230 covering part of the device 234. An electrode 238 extends from the transparent electrode 230 for connecting a device 234 to an external device (not shown). For example, the transparent electrode 230 is made of indium tin oxide (ITO) and the electrode 238 is made of aluminum (Al). In such example, the device 234 and the transparent electrode 230 is covered entirely by barrier layers 252, 260 and an intermediate layer 256, whereas the electrode 238 is partially covered by the barrier layers 252, 260 and the intermediate layer 256. The intermediate layer 256 may be a polymer layer or a decoupling layer, deposited to flatten the vertical profile of the device 234 and other layers deposited thereon.
When depositing the barrier layers 252, 260 on the device 234 by sputtering or CVD, one or more of the barrier layers (e.g., the third layer 260) may have insufficient thickness at the vertical slope as shown in circle 222. Such barrier layers may provide insufficient protection against moisture or oxygen at these edges. Further, one or more of the barrier layers (e.g., the third layer 260) may have insufficient horizontal coverage at the edges, allowing moisture or oxygen to seep through the interfaces (as shown in circles 218 and 226) and come in contact with the device 234. Another defect may be caused during the removal of the shadow mask 110. That is, the removal of the shadow mask 110 may cause the barrier layers to be delaminated and torn apart as shown in circle 214. Finally, barrier layers formed by sputtering or CVD may suffer cracks that may extend through the thickness of a barrier layer as shown in circle 210.